Continuous stirred tank reactors offer distinct advantages over batch-type reactors for a wide variety of hydrocarbon oxidations, such as those involving gas-liquid reactions as well as those involving gas-liquid-solid reactions. For example, it is generally the case that the capital investment expenses as well as the operating costs are typically relatively lower for a conventional continuous stirred tank reactor than for a conventional batch-type reactor of comparable throughput.
There are certain instances, however, where a batch-type reactor is preferred over a continuous stirred tank reactor. For example, in the manufacture of certain aromatic carboxylic acid products, it is well known that the presence of the product causes inhibition of the oxidation reaction itself, depending upon the concentration of the products within the reaction mixture. Thus, in many instances involving product-inhibited oxidation reactions the utilization of a single stirred tank reactor cannot provide the high yields desired because of the presence of a relatively higher concentration of the inhibiting product during much of the oxidation reaction period. While a batch-type reactor offers one advantage over a continuous stirred tank reactor in this regard, in that the inhibiting product is typically not present in sufficient reaction-inhibiting concentration until towards the end of the reaction, certain disadvantages of utilizing batch-type reactors generally favor utilization of a continuous stirred tank reactor, if at all possible. For example, it is well known that product quality generally varies from batch-to-batch. Occasionally, the variation in product quality renders the product unacceptable for its intended purpose. Also, it is generally well recognized that batch-type operations typically involve relatively greater manpower expenses and batch-type reactors are typically larger than continuous reactors for the same throughput.
While it is possible to connect a large number of continuous stirred tank reactors in series to achieve desired reaction kinetics, to do so is not economically practical from the standpoint of capital-investment and operating cost considerations.
Liquid phase oxidation of an alkylaromatic is exothermic. Certain conventional processes for oxidizing an alkylaromatic in the liquid phase employ a reaction mixture which includes a solvent. In such processes, a desired reaction temperature is achieved by maintaining the oxidation-reactor internal pressure at a value such that evaporation of a portion of a reaction mixture occurs at a desired rate. The thus-vaporized portion of the reaction mixture is then passed from the oxidation reactor to a condenser which serves to remove heat of reaction and to condense at least a portion of the reaction-mixture vapor supplied thereto. The condensate that it produced is then typically returned to the reactor as reflux.
The liquid phase oxidation of aromatic alkyls to aromatic carboxylic acid products is currently of significant commercial importance. It is accordingly highly desirable to improve the yield and quality of aromatic carboxylic acid products.